The invention relates to propulsion apparatus for an all terrain vehicle, particularly a crawler track amphibious vehicle adapted to traverse marginal terrain and water as found in polar regions.
The present applicant has U.S. Pat. Nos. 4,645,023 and 4,727,949 which relate to an all terrain vehicle and method of operating same respectively, which are closely related to that present invention. Similarly to the patented vehicle, the present invention is a vehicle combination having first and second vehicle units interconnected by an articulated link. Each vehicle unit has a pair of spaced crawler tracks which, in combination with the articulated link, permit the vehicle combination to perform maneuvers for negotiating steep and marginal terrain, including water and ice, which would normally not be negotiable by a single vehicle unit of this type.
Each patented vehicle unit has body portions provided with forward and rear sprockets which engage the crawler tracks to power the vehicle. Lower portions of the body have generally flat centre sections and flat upwardly extending forward and rear body portions which terminate adjacent the forward and rear sprockets. The generally flat center portion of the body carries a plurality of free-wheeling track rollers which engage the track and reduce friction between the crawler track and body. In certain situations, difficulties can arise in maintaining track alignment with the rollers engaging lower portions of the tracks. Also, in marine applications, corrosion of the track rollers is a problem.
All track laying vehicles known to the applicant usually have a lower portion of the body provided with a generally flat central portion, with flat, upwardly extending forward and rear portions which resemble those shown in the patented vehicle. A problem common to all track laying vehicles is the working life of the crawler track assembly itself. Metal link chains, in which a plurality of links are inter-connected by link pins, wear excessively in abrasive conditions, such as found when traversing swamps, muddy or sandy areas, etc. Furthermore, such metal tracks, particularly when used in the salt water, corrode rapidly. Many different types of track belt assemblies have been used to overcome these problems, such as strips of so-called rubber belt material.
It is important that the crawler tracks maintain alignment with the sprockets during operation of the vehicle, so that the track is not "thrown" from the sprockets. The ability of a track to run on its sprockets is termed "track stability" or "track alignment" and, in general, the higher the track tension, the higher the track stability. Track tension is the tensile force in the track or belt that is applied by moving one of the sprockets relative to the other sprocket to apply a sufficiently high load on the track to maintain the track running aligned on the sprockets. For most types of crawler track assemblies it is known that track tension is a major contributor to wear of the tracks, irrespective of all the other factors contributing to crawler track assembly wear. Furthermore, high track tension consumes more power from the power train than low track tension, and thus reduces overall efficiency of operation of the vehicle. If a means of reducing track tension can be found, operating efficiency and life of the track assembly will be increased.
U.S. Pat. No. 3,842,785 (Rivet) discloses an amphibious marsh craft in which lower runs of crawler tracks are guided in channels extending longitudinally along a lower surface of a pair of spaced apart sponsons, thus eliminating the more normal track rollers. This vehicle is designed for marsh use, and it would appear that the crawler tracks are the only mode of propulsion. Because conventional crawler tracks perform very inefficiently in water, conventional amphibious track-laying vehicles commonly have an auxiliary marine propeller fitted for water use. However, propeller-powered vehicles used in polar regions are vulnerable to propeller damage due to ice contact. A water jet can be substituted to reduce this problem, but a water jet powered vehicle used in very low temperatures is susceptible to ice blocking the intake of the water jet, preventing further operation until the blockage has been cleared.